A portion of the disclosure of this patent document contains material which is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever.
The present invention relates to pick and place machines. More particularly, the present invention relates to an improved vision system for pick and place machines.
Pick and place machines are used by the electronics assembly industry to mount individual components on printed circuit boards. These machines automate the tedious process of placing individual electrical components on the circuit board. The machines generally pick up individual components from a component feeder or the like, and place the components in their respective positions on the circuit board.
In operation, it is generally necessary for the pick and place machine to review a given component prior to placement in order to adjust the orientation of the component for proper placement. A number of systems are known which allow the pick and place machine to review the component for the purpose of assessing its current orientation and computing an indication of how to adjust the orientation of the component in order to precisely place it on a PC board. Such systems generally fall within one of two categories.
The first type of system is known as an off-head system. These systems generally provide a fixed optical sensor, such as a two-dimensional (2-D) camera, that is located at a specific position relative to or within the pick and place machine. Once a component is picked up from the component feeder, it is typically moved to the location of the fixed optical sensor such that the orientation of the component can be computed from the image provided by the optical sensor.
The second type of system is known as on-head sensor system as described in U.S. Pat. No. 4,615,093 to Tewes. These systems, sometimes called xe2x80x9con-the-flyxe2x80x9d, have an optical sensor that is mounted to the component head of the pick and place machine. Thus, the optical sensor of the on-head system essentially rides with the component(s) from the component feeder to the desired mounting location(s). While travelling, the on-head sensor can image the components such that component orientations can be determined, and adjusted while the head is moving. Such systems provide a number of advantages over off-head systems. One such advantage is that precious assembly time is not sacrificed by moving the head to an off-head inspection location prior to mounting. Given that pick and place machines place a great number of components per hour, this time savings is significant.
One specific vision system, the on-head linescan sensor, provides significant advantages over various other systems. Such advantages include increased throughput, and manufacturing flexibility. On-head linescan sensors are mounted to, and travel with a placement head of the pick and place machine. Machines incorporating on-head linescan sensors are faster than off-head sensor systems since the head does not need to travel to a fixed inspection station to compute component orientation. Such machines are also very flexible due to the fact that they can directly image the electrical contacts of a wide array of components such as chip capacitors, flip-chips, Chip Scale Packages (CSPs), Ball Grid Arrays (BGAs), Quad Flat Packs (QFPs), and connectors. Additionally, since the linescan sensor scans line by line, the field of view is highly variable, and thus easily adaptable to many different applications. Further, since image resolution is related to sensor scan speed, image resolution can be varied as desired. Although on-head linescan sensors represent a significant improvement, pick and place machines employing such sensors do not provide the level of flexibility and placement efficiency that could be realized.
A pick and place machine is disclosed which includes an on-head linescan sensor, and at least one additional optical sensor. The linescan sensor provides component data, in the form of information for orienting the component or of quality-related information about the component. The at least one additional sensor can be an off-head linescan sensor, an off-head or on-head 2-D camera, an on-head shadow (e.g. one which shadows or images the profile of a component onto a detector, such as a LaserAlign(copyright)) sensor, an off-head or on-head coplanarity sensor, or an on-head or off-head fiducial camera. The additional optical sensor is disposed to provide essential placement information in the form of orientation information or inspection information. Combinations of the aforementioned additional sensor can also be used in embodiments of the present invention to the pick-and-place machine. The present invention is particularly useful with multi-head component placement machines, although it is usable with single head machines as well.